Nukes' Architecture Unveiled

Use each technology for what it does the best

We chose JMX to manage Nukes components to provide hot deployment and
component decoupling. This means a component can be removed from the system
while it is running with little or no consequence. A webpage is made of several
tiles, and each "tile" is a component/block/module package. We also wanted to
support completely dynamic web sites, so you can add new modules to a running
instance without service disruption. The jboss-system module
built on top of core JMX brings us more features than plain vanilla JMX, like
service dependencies. Therefore, each component is an MBean service hooked in
JBoss. The original PostNuke components have a lifecycle, but they do not
handle dependencies at all. Nukes does, leveraging a typical J2EE
specification with some JBoss flavor.

In our port we split data and made a clean separation between management
model and the business model. Usually business data need to be scalable and
highly configurable, so they are often made of entity EJB components. Our
infrastructure leverages the local interfaces introduced since EJB 2.0 because
we stay in the same VM all the time. We colocate the web server and the
component containers in the same space, avoiding excessive serialization. We
do not use data patterns such as DAO or DTO, preferring to use JBoss in its
default local mode.

Because of the JMX architecture decision, the hardcore management data is
exposed as MBeans attributes. We saw how to change the site name and the site
slogan, but you can configure Nukes further this way. Each MBean attribute is
persisted in the relational database as well, avoiding the loss of
configuration when you restart the server.

Nukes Component Development

It is easy to create a Nukes component from scratch. We are going to create
a small module.

Module invocation

Since a module is more or less a set of operations, we need a standard way
to invoke them. We chose to keep the original way that PostNuke authors decided
to specify invocations in URL syntax. It looks deceptively standard. Each
action on a module is triggered when you call a URL that looks like this:

That URL triggers the operation operation_name on the module
module_name. The two parameters, module and
op, tell Nukes which operation to invoke on what module. The other
parameters can be fetched by the module by introspection when it is invoked.
Since a module is a JMX MBean, each managed operation that follows the right
pattern may be invoked in this manner. This spells out an invocation that the
JMX server can apply on a target MBean. Behind the scenes, we translate a URL
invocation in a JMX invocation in memory. It is fast and follows the same
naming patterns.

public void operation(org.jboss.Nukes.html.Page page)

If you type the URL with the value of the op parameter as
operation, Nukes will call that method on your module object.

Module Creation

PostNuke's module model is almost identical to the servlet model. You code
your page behavior in pure Java. We prefer this to the JSP Model 2
architecture. Let's start with the TemplateModule class
declaration:

The Page object is provided as a parameter by the core and is
used by this method to render the HTML content. In this Nukes operation, the
HTML rendered form carries an URL that will activate the method
action of the module Template.

Let's see the action method declared by the
Template module:

/**
* This method is called with the following url:
* http://localhost:8080/Nukes/index.html?module=template&op=action
*/
public void action(Page page)
{
// get the parameter
String name = page.getParameter("name");
// if no name has been provided, just render the main page again
if (name == null || name.length() == 0)
{
main(page);
return;
}
page.print(&quot;<div align=\"center\">&quot;);
page.print("Welcome to the template module " + name);
if ( getApi().userLoggedIn() )
{
page.print("you are logged in");
}
page.print(&quot;</div>&quot;);
}

This method uses Page as a context object because it stores the
HTTP parameters like the HttpRequest object in the servlet API.
You can use the Page API as you do in the servlet API. Another
object that is used by this method is the Api object returned by
the getApi() method. It provides services a component may need.
In this case it is used to know whether a user is logged in or not and to
display a message.

Module packaging

The final step in our module creation is deployment. We have to tell JBoss
that the class we just wrote is a Nukes module. The
jboss-service.xml file declares a Nukes module using the class we
just examined.

Then we package the class in a jar archive and we add a file
jboss-service.xml in the META-INF directory of that
archive. Packaging the file is done with the command jar -cvf
Nukes-template.sar *. The special extension .sar tells
JBoss that the packaged file is a service archive.

Figure 7 — the module packaged for deployment

Finally we copy that file into the JBoss deploy directory, where it is
automatically deployed. The module can be used without restarting Nukes.
Deployment is totally dynamic and is done at runtime.

Figure 8 — the template module is deployed

Final words

What did we learn from our experience? Software that exists is a good place
to start even if it is in another language and we are Java snobs. The second
lesson was that PHP/PostNuke isn't really designed to handle very high loads.
We decided to port to J2EE and leverage many of the existing APIs (JMX and EJB)
to provide a straight port of PHP technology that became "enterprise level"
almost immediately. That was the real lesson for us, a proof that all the work
we do on system level Java pays off in spades at the application level.

Today, the product is maturing. We've ported the majority of the original
PostNuke modules and enhanced some of them along the way. Nukes is production
ready — it's in production. It has powered the JBoss.org web site for three months without major problems. Its advanced architecture makes it very
scalable and easy to work with. We welcome you to come and help us with the
porting of modules so we can finally have a decent CMS/Portal base in Open
Source Java.

Marc Fleury
, Ph.D., is CEO of JBossGroup, LLC. and founder of the JBoss open-source project.